IL1R1 and acute myocarditis: As a positive regulator, IL1 upregulates MAPK and NFkB signaling pathways via myeloid differentiation factor-88 (MyD88) (Van Tassell et al., 2015), and both IL1R-/- and MyD88-/- mice display reduced fibrosis and progression toward heart failure in a model of acute myocarditis (Blyszczuk et al., 2009).